Heat-treating furnace



Aug. '10, 1948. H, D BRIN 2,446,642

HEATS-TREATING FURNACE 3 Sheets-Sheet 1 Filed March 27, 1945 WITNESSES:I Q INVENTOR fiwfiywv.

ATTORNEYS.

Aug. 10, 1948. H. DOIBRINI 6,

' HEAT-TREATING FURNACE Filed March 27, 1945 a Sheets-Sheet 2 @MWH RINVENTOR I Mun- Aq nrrok/v H. DOBRIN HEAT- TREATING FURNAC E Filed March27, 1945 3 Sheets-Shet 3 INVENT R.

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EMT-THING NACE Harry Dobrin, Pittsburgh, Pa assignor to Furnace eers,Hue... Pittsburgh, Pa.

Application March 21.1945, Serial No. 585,149

.by the heat input and the exhaust are regulated simultaneously. Otherobjects are to providesuch a furnace in which the natural draft throughthe furnace is reduced during periods of low burning, and inwhich a hightemperature is main tained in. the lower part of the furnace at alltimes. I The preferred embodiment of the invention is illustrated in theaccompanying drawings in which Fig. 1 is an end view of my furnace; Fig.2 is a longitudinal section taken on the line 11-11 of Fig. I; Fig. 3 is'a horizontal section taken on the line III-III of Fig. 2, but with theburners omitted; Fig. i is an enlarged end view of one of the eductorsfor exhaust gases; and Fig. 5 is an enlarged longitudinal sectionthrough an eductor.

Referring to the drawings, a heat treating furnace of the bell type isshown in which therefractory walls and roof, collectively designated l.are supported in a structural steel frame 2 so that the furnace can belifted by a crane from a suitable base 3 in order to permit charges ofmetal to be placed on the base for heat treatment. For example. coils ofwire or flat strip (not shown) may be stacked on the base and thencovered with protective hoods l that areshown in section in Fig. 3 andin broken lines in Fig. 2. The furnace is then lowered over the hoodsuntil it rests on the floor around them, whereupon it is ready foroperation. The walls of the furnace are provided near its bottom with aseries of laterally spaced burner openings 6 and i into which burnersare directed. Preferably, the burners burn gas and are of the kinddisclosed and claimed in my copending application Serial No.'554,876,filed September 20, 194,-now Patent No. 2,403,431, granted July 9, 1946.Each burner includes a main burner ii that burns gas mixed with primaryand secondary air, and a secondary burner a above it that burns raw gaseither at the same pressure as or at a lower pressure than the gassupplied to the main bumer. The secondary air enters the outer end ofopenings 6 in the space around the main burners. These burners areconnected to a gas pipe ii that extends around the furnace and that isconnected by a pipe ii to the main source of gas pp y- In pipe l2 thereis a throttling valve 83 by which the flow of gas to the burners iscontrolled.

N Cms. (Cl. 158-1) The stem of this valve is provided with a laterallyprojecting arm is by which the stem can be turned to adjust the size ofthe opening through thevalve. The valve stem end or the arm isadjustable in any suitable manner around the adjoining stem so that forany'given-position of the arm the valve may have any desired degree ofopening. The outer end of arm is is pivotally connected to the lower endof a link 16 the upper end of which is pivotally connected to an arm llprojecting laterally from an oscillatabl member is mounted in anelectrically or pressure open-- ated valve-actuating device l9 of knownconstruction. If electrically operated, this device is electricallyconnected to and operated by suitable temperature responsive means iil(Fig. 2) disposed inside the furnace, whereby member it is turned oneway or the other, depending on whether the furnace is calling for heator is becoming too hot.

In order to control the flow of hot gases in the furnace, and toeliminate the necessity for burners in the center of the furnacechamber, a plurality of exhaust conduits ii of any suitablecross-sectional shape extend down through the roof of the furnace alongits center. However, in some cases it may be desirable to. place theexhaust conduits at the ends or sides of the furnace. The open lowerends of these conduits are spaced a short distance from the floor of thechamber so that the hot gases that rise from the burners are drawntoward the middle of the furnace and down around hoods i to the bottomof the exhaust conduits to keep the lower part of the furnace hot, Theproducts of combustion within the furnace are positively drawn outthrough conduits ill by means of air-operated. eductors mounted on theupper ends of the conduits 'above the furnace roof.

In accordance with this invention each eductor includes a Venturi tube32 forming a continuation of th adjoining conduit 3!, the tube beingencircled behind its narrowest part or throat by a ring 33 weldedthereto in order to form a chamber 3d around the tube. The front wall ofthis chamber, inside the tube, is provided with a plurality ofcircumferentially spaced jet holes 35 directed forward. Ring 33 isprovided with a laterally projecting coupling 36 connected by a branchpipe 37 to a main pipe 38 that in turn is connected to a suitable sourceof air supply, such as a continuously operating'blower 39. Air enteringeductor chambers 3t escapes through jets 35 into the Venturi tubes andthus draws exhaust gases up through conduits 3| from within the furnace.The greater the air flow through the eductors the more-rapidly theexhaust gases are drawn out of the furnace.

'nace.

section of air pipe II above the gas regulating valve. The stem of thisvalve likewise is provided with an adjustable arm 42. generally parallelto arm H, and pivotally connected by a link II at its outer end to armI! of valve-controlling device i8, when this regulating mechanism isinstalled, the stem of the air valve is adjusted relative to its controlarm so that the proper volume of air will be delivered to the eductorsfor any given amount of gas supplied to the burners.

In operation, when temperature responsive means 20 inside the furnacecalls for heat, valveactuating device It will be operated by it to swingarm I! vertically in order to move links it and 43 in the direction thatwill cause arms ll and 42 to open the gas and air valves farther. Thus,as the burners operate at higher capacity the eductors likewise do thesame, so the combustion gases inside the furnace are withdrawn at ahigher rate in keeping with the higher rate at which they are produced.When the furnace temperature starts to become too great, the gas and airvalves are turned down simultaneously in the same manner.

Another feature of this invention is that the lower part of the furnaceis kept from becoming unduly cool when the burners are turned low aftertheupper part of the material being heat treated has reached the desiredtemperature, whereby the lower part of the material is brought up totemperature soon after the upper part. Accordingly, means is providedfor reducing the natural draft through the furnace so that there willnot be enough cold air drawn in through burner openings 6 to materiallyreduce the temperature in the lower part of the furnace. This desirableresult is accomplished by directing a stream of air down into eacheductor during low burning periods to counteract the upward draft thatdraws air in through burner openings 8. For this purpose an L-shapenozzle I is welded in each eductor tube 32 near its outer end with theinner end of the nozzle directed downwardly toward the throat of thetube. The outer end of the nozzle is threaded and coupled to a branchpipe extending laterally from a main pipe 52 above the fur- One end ofthe main pipe extends down the end of the furnace and connects with airpipe 38.

The horizontal section of pipe 52 at the end of the furnace is providedwith a valve 53 having a stem to which an arm 54 is adjustablyconnected. The outer end of this arm is connected by a link 58 with asecond arm 5'! mounted on the oscillatable member is of valve controller19. Valve 53 is set so that it does not open until after the other airvalve 4| has closed. Gas valve l3 can not be closed completely. Withthis arrangement of valves a back pressure is created in the eductors assoon as the air supply to jets 35 is cut oil, which occurs when theburners are turned low by valve 13. This back pressure prevents anundesirable amount of cold air from being drawn into the furnace throughburner openings 6, but it does not shut off all draft up through theeductors. Consequently, the temperature of the lower part of thematerial being heat treated is raised much more quickly than it would beif large amounts of cold air were allowed to be drawn into the bottom ofthe fur- This increases the tonnage of material that can be heat treatedin this furnace per day, and thereby reduces its costper ton.

According to the provisions of the patent statutes. I have explained theprinciple and construction of my invention and have illustrated anddescribed what I now consider to represent its best embodiment. However,I desire to have it understood that, within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallyillustrated and described.

I claim:

1. In a heat treating furnace, walls defining a heating chamber, aburner therefor directed into the lower portion of the chamber, aconduit for supplying fuel to the burner, said chamber having an openinlet for secondary air for the burner and also having an outlet forexhaust gases, an air-operated eductor connected to said outlet, aconduit for supplying air to the eductor, means responsive totemperatures in said chamber for controlling the flow of fuel to saidburner and air to said eductor to thereby increase said air flow whensaid fuel flow is increased. and means for directing a stream of airbackwardly in the eductor to retard the flow of exhaust gasestherethrough when said fuel flow is at a minimum and said air flow tothe eductor is substantially stopped.

2. In a heat treating furnace, walls defining a heating chamber, aburner therefor directed into the lower portion of the chamber, saidchamber having an open inlet for secondary air for the burner and alsohaving an outlet for exhaust gases, a fuel line connected to the burner,an eductor connected to said outlet, an air pressure line connected tosaid eductor for operating it, throttling valves in said fuel and airlines, valveactuating means operatively connected to said valves, meansresponsive to temperatures in said chamber for operating saidvalve-actuating means, whereby to increase the air flow to the eductorwhen the fuel flow to the burner is increased, and means for directing astream of air backwardly in the eductor to retard the flow of exhaustgases therethrough when said fuel flow is at a minimum and said air flowto the eductor is substantially stopped.

3. In a heat treating furnace, walls defining a heating chamber, aburner therefor directed into the lower portion of the chamber, aconduit for supplying fuel to the burner, said chamber having. an openinlet for secondary air for the burner and also having an outlet forexhaust gases, an air-operated eductor connected to said outlet, aconduit for supplying air to the eductor, means responsive totemperatures in said cham- .ber for controlling the fiow of fuel to saidburner and air to said eductor to thereby increase said air flow whensaid fuel flow is increased, a nozzle directed backwardly into theeductor, an air pressure line connected to said nozzle, a normallyclosed valve in said air line, and means for opening said valve whensaid fuel flow is at a minimum and said air flow to the eductor issubstantially stopped.

4. In a heat treating furnace, walls defining a heating chamber, aburner therefor directed into the lower portion of the chamber, saidchamber having an open inlet for secondary air for the burner and alsohaving an outlet for exhaust gases, a fuel line connected to the burner,an eductor connected to said outlet, an air pressure line connected tosaid eductor for operating it, throttling valves in said fuel and airlines, valve-actuating means operatively connected to said valves, meansresponsive to temperatures in said chamber for operating saidvalve-actuating means, whereby to increase the air flow to the eductorwhen the fuel flow to the burner is increased, a nozzle directedbackwardly into the eductor, and air pressure line connected to saidnozzle. a normally closed valve in said nozzle air. line. and meansoperatively connecting said valve-actuating means to said last-mentionedvalve for opening it when said fuel flow is at .'a minimum and said airflow to the eductor is sub stantially stopped.

5. In a heat treating furnace, walls defining a heating chamber providednear its bottom with a burner port, a burner adjacent the outer end ofsaid port with a space between it and the port for admission ofsecondary air, a fuel line connected to the burner, an exhaust conduitextend.-

ing out of said chamber with its inner end dis-' posed near the chamberbottom, an eductor for exhaust gases connected to the outer end of saidconduit, an air pressure line connected to said eductor for operatingit, throttling valves in said fuel and air lines, a nozzle directedbackwardly into the eductor, an air pressure line connected to saidnozzle, a normally closed valve in saigl nozzle air line,valve-actuating means operativel connected to said valves, and meansresponsive to temperatures in said chamber for operatingsaidvalve-actuating means, said throttling valves being adjusted inunison toward closed and wide open positions, and said normallyclosed'valve being opened only after said throt tling valves have been closedsumciently to re duce said fuel flow to a minimum and to sub.-stantlally cut off the air fiow through said firstmentioned air line.

6. In a heat treating furnace, walls defininga heating chamber, a burnertherefor directed,

pressure line connected to said eductor for op-" crating it, throttlingvalves in said fuel and air lines, valve-actuating means, meansresponsive to temperatures in said chamber for operating said actuatingmeans, and mechanical means operatively connecting said actuating meansto said valves whereby to increase the air flow to the eductor when thefuel flow to the burner is increased. 7. In a heat treating furnace,walls defining a heating chamber, a burner therefor directed into thelower portion of the chamber, a fuel line connected to the burner, anexhaust conduit extending out of said chamber, an eductor for exhaustgases connected to said conduit, an air pressure line connected to saideductor for operating it, throttling valves in said fuel and air lines,valve-actuating means having an electrically operated valve-actuatingmember, means responsive to temperatures in said chamber for controllingthe movements of said member, links pivotally connected to said member.and control arms for said valves pivotally coected to said links,whereby said actuating me opens both valves simultaneously.

8. In a heat treating furnace, walls defining a heating chamber, aburner therefor directed into the lower portion of the chamber, a fuelline connected to the burner, an exhaust conduit extending out of saidchamber, a Venturi eductor tube mounted on the outer end of said conduitand provided at its throat with a plurality of circumferentially spacedjet openings directed forward inside the tube, said tube being providedwith a chamber surrounding the inlet ends of said Jet openings. an airline connected to said tube chamber, throttling valves in said fuel andair lines, valve-actuating means, means responsive to temperatures insaid chamber for operating said valve-actuating means, and meansoncratively connecting said actuating means to said valves whereby toincrease the air flow to said tube chamber when the fuel flow to theburner is increased.

9. The combination with a heat treating furnace, a burner therefordirected into the lower portion of the chamber, a fuel line connected tothe burner, a throttling valve in said line. means responsive to thetemperature inside the furnace for controlling said valve, and anexhaust conduit extending out of the furnace, of a Venturi eductor tubeconnected to said conduit iii) and comprising a forwardly taperedtubular rear portion encircled by a ring forming therewith an annularchamber having a substantially flat front wall provided with a pluralityof circumferentially spaced jet openings directed forward, said tubehaving a rearwardly tapered front portion secured to said wall aroundsaid jet openings, an air pressure line connected to said annularchamber, a throttling valve in said air line, and means operablyconnecting said temperature responsive means to said air valve wherebyto increase the air flow to the eductor when the fuel flow to the burneris increased.

10. The combination with a heat treating furnace, a burner therefordirected into the lower portion of the chamber, a fuel line connected tothe burner, a throttling valve in said line, means responsive to thetemperature inside the furnace for controlling said valve, and anexhaust conduit extending out of the furnace, of a Venturi eductor tubeconnected to said conduit and comprising a forwardly tapered tubularrear member encircled by a ring forming therewith an annular chamberhaving a substantially flat front wall provided with a. plurality ofcircumferentially spaced jet openings directed forward, a rearwardlytapered tubular front member secured to said wall around said jetopenings, a nozzle mounted in the wall of said front member near itsfront end and pointing backwardly toward its rear end, air pressurelines connected to said nozzle and annular chamber, valves in said airlines, and means operatively connecti said temperature responsive meansto said air valves.

HY DOBRIN.

REFERENCES CE'K'ED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,814,567 Merkt July 14, 19311,848,184 Mowha Mar. 8, 1932 1,937,974 McKee Dec. 5, 1933 2,042,475Meharg et al June 2, 1936 2,069,542 Soubier Feb. 2, 1937 2,193,185Weaver Mar. 12, 1940

